Adenosine metabolism

Figure 12.2 Adenosine metabolism. Intracellular adenosine concentrations depend on the balance between energy storage and breakdown. The most important enzymes catalyzing the reactions are indicated. SAH, S-adenosyl-homocysteine ENTs equilibrative nucleoside transporters CNTs, concentrating nucleoside transporters.

Adenosine metabolism (Fig. 12.2) is reviewed in Dunwiddie Masino (2001) and Ribeiro et al. (2002). The phosphorylation of intracellular adenosine to AMP is catalyzed by adenosine kinase. Intracellularly, adenosine can also be deami-nated to inosine by adenosine deaminase. Free intracellular adenosine is normally low. Excess adenosine, which cannot be regenerated to ATP, is extruded to the extracellular space by equilibrative nucleoside transporters (ENTs) in the cell membrane. During electrical stimulation or energy depletion, adenosine is... 

Chagoya de Sanchez V., Hernandez-Munoz R., Suarez J. et al. (1996). Temporal variations of adenosine metabolism in human blood. Chronobiol Int. 13,... 

Kobayashi S, Zimmermann H, Millhorn DE (2000) Chronic hypoxia enhances adenosine release in rat PC 12 cells by altering adenosine metabolism and membrane transport. J Neurochem 74(2) 621-632... 

The accumulation of adenosine in hypoxia is at least partially explained by hypoxia-mediated regulation of enzymes that are involved in adenosine metabolism (i) adenosine kinase (Decking et al. 1997) and (ii) 5 -nucleotidase (Headrick and Willis 1989 Kobayashi et al. 2000 Thompson et al. 2004). In particular, adenosine can be generated extracellularly through the hydrolysis of released nucleotides by ecto-5 -nucleotidases (Dunwiddie et al. 1997) or can be produced in the cytosol and transported to the extracellular space (Higgins et al. 1994). 

Gaitanaki, C. Beis, I. (1985). Enzymes of adenosine metabolism in Hymenolepis diminuta (Cestoda). International Journal for Parasitology, 15 651-4. 

CYCLOPHOSPHAMIDE PENTOSTATIN t risk of potentially fatal cardiac toxicity Attributed to interference of adenosine metabolism by cyclophosphamide Avoid co-administration... 

As with almost all systemic fungicides, after foliar or soil application, absorption and translocation via the xylem follows. The mechanisms of action of pyrimidines are not very clear, however, information suggests that spore germination and mycelial growth are inhibited. In addition, studies with ethirimol suggest that it inhibits RNA synthesis as well as adenosine metabolism by blocking adenosine deaminase. 

Nees, S and Gerlach, E, Adenine nucleotide and adenosine metabolism in cultured coronary endothelial cells. In Regulatory functions of adenosine, (eds. Berne, RM, Rail, TW and Rubio, R), Martinus Nijhoff Publishers, The Hague, 1983,347-360. 

Dawicki DD, Agarwal KC, Paries RE, Jr, Adenosine metabolism in human whole Mood Effects of nucleosicb transport inhibitors and phosphate concentration, Biochem. Pharmacol., 1988,37 621-626. 

Klabunde, RE, Dipyridamole inhibition of adenosine metabolism in human blood, Eur. J. Pharmacol, 1983,93 21-26. 

The low RBC ATP concentration is the most probable explanation for the hemolysis (1). In vitro studies of adenosine metabolism by intact patient s RBC showed as expected, a markedly decreased ATP synthesis from adenosine moreover, metabolic studies of adenylic nucleotides labelled with radioactive adenine indicate that AMP degradation (probably by hydrolysis of the phosphate ester followed by deamination of adenosine) is abnormally elevated in the patient s erythrocytes. Thus, the low RBC ATP concentration appears to be secondary to both a diminished synthesis of AMP from adenosine and an excessive catabolism of AMP. 

EFFECT OF HORMONES ON ADENINE AND ADENOSINE METABOLISM IN MAMMARY GLAND IN VITRO... 

The rate of adenosine metabolism was enhanced, when insulin was used with prolactin and hydrocortisone, and it was highest when both of these hormones were added together (Table 4). 

Table 3 Adenosine metabolism in mammary gland explants of pregnant mice treated with various hormones...

Case RB, Felix A, Wachter M, Kyriakidis G, Castellana F (1978) Relative effect of CO2 on canine coronary vascular resistance. Circ Res 42 410-418 Dawes GS (1941) The vaso-dilator action of potassium. J Physiol London 99 224-238 Degenring FH, Curnish RR, Rubio R, Berne RM (1976 Effect of dipyridamole on myocardial adenosine metabolism and coronary flow in hypoxia and reactive hyperemia in the isolated perfused guinea pig heart. J Molec Cell Cardiol 8 877-888 Driscol TE, Berne RM (1957) Role of potassium in regulation of coronary blood flow. Proc Soc Exptl Biol Med 96 505-508... 

Kiibler WP, Spieckermann PG, Bretschneider HJ (1970) Influence of dipyridamole (Persantin) on myocardial adenosine metabolism. J Mol Cellular Cardiol 1 23-38... 

Mustafa SJ, Berne RM, Rubio R (1975) Adenosine metabolism in cultured chick-embryo heart cells. Am J Physiol 228 1474-1478... 

Adenosine deaminase plays a key role in adenosine metabolism. This nucleoside has some important pharmacological and toxic effects. An adenosine deaminase deficiency observed in some cases of severe con-... 

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